362 



PRACTICAL PHYSIOLOGY 



showing that the convulsions were due to the action of the drug upon 

 the nerve-cells and dendrites in the spinal end. 



Record of a Voluntary Contraction. If a finger be placed upon a 

 muscle voluntarily thrown into contraction, a series of vibrations can be 

 felt. These can be recorded and their rate determined in the following 

 way. 



A receiving tambour, with a button or a piece of cork fixed upon the 

 rubber membrane, is connected with a bellows recorder (Fig. 239), 



Fio. 239. Brodie's bellows recorder. The bellows are made of aluminium plates and 

 peritoneal membrane. 



which is arranged to write upon a revolving drum. A chronograph 

 is set up for marking the time in seconds. The button of the tambour 

 is placed upon the adductor pollicis, or the masseter muscle of the 

 subject. When the muscle is voluntarily contracted the lever shows 

 a number of vibrations; these are recorded (Fig. 238). The curve 

 obtained resembles an incomplete tetanus with 6 or 8 vibrations per 

 second. 



CHAPTER XXXIII. 



THE FUNCTIONS OF THE ANTERIOR AND POSTERIOR ROOTS OF 

 THE SPINAL CORD. THE BELL-MAJENDIE LAW. 



THE researches of Bell and of Majendie showed that the anterior 

 roots of the spinal cord were motor, and the posterior were sensory ; the 

 former nerves are efferent, carrying nervous impulses from the spinal 



